Trump revoked Brennan's clearance for what he called "unfounded and outrageous allegations" against his administration, while also announcing that the White House is evaluating whether to strip clearances from other former top officials. 

Trump later told the Wall Street Journal his decision was connected to the ongoing federal probe into alleged Russian interference in the 2016 election and allegedly collusion by his presidential campaign.

"I call it the rigged witch hunt, (it) is a sham," Trump said in an interview with the newspaper on Wednesday. "And these people led it."

"It's something that had to be done," Trump added. -Reuters

Writing in the New York Times, Brennan - who led the CIA under President Obama, called Trump's denials of collusion with Russia "Hogwash," and vowed not to be silenced.

"The only questions that remain are whether the collusion that took place constituted criminally liable conspiracy, whether obstruction of justice occurred to cover up any collusion or conspiracy, and how many members of 'Trump Incorporated' attempted to defraud the government by laundering and concealing the movement of money into their pockets," Brennan wrote in the Times.

Mr. Trump clearly has become more desperate to protect himself and those close to him, which is why he made the politically motivated decision to revoke my security clearance in an attempt to scare into silence others who might dare to challenge him. -John Brennan